The man who masterminded London's highly successful Olympic Games has said power blackouts would be "the best possible thing" because they would force politicians to confront the looming energy crisis.

Sir John Armitt, who is also advising the Labour Party on Britain's infrastructure needs, said the country was heading towards an energy-capacity crunch because ministers had failed to ensure the construction of new power stations to take over from decommissioned nuclear and coal plants.

And as Britain faces a weekend of freezing weather there were new warnings about the proximity of a capacity crunch from Dieter Helm, a leading energy academic who believes ministers have underestimated future power demand.

Angry business leaders dismissed Armitt's comments as irresponsible, but Armitt, who worked on the Sizewell-B nuclear reactor while at the construction group Laing, insisted new capacity was needed.

"In harsh political terms [blackouts] would be the best possible thing that could happen because this country is extremely good in a crisis," he told the construction industry magazine Building.

He added: "We are very close to being in a crisis when it comes to energy … the Central Electricity Generating Board used to say that a resilient network operated on a 25% capacity surplus. We're down to 4% because we've gone slower than we should have done on nuclear."

His warning was given new impetus by Helm, who cited calculations by the Aurora Energy Consultancy, which show surplus energy capacity in 2015-16 could be close to zero – leaving the nation on the cusp of blackouts.

"We know what the calculations are on the supply side because no new kit [power plants] will be built before 2015-16, but on the supply side all official estimates have underestimated GDP [gross domestic product] growth and therefore energy demand," said Helm, who is professor of energy policy at Oxford University.

"The government must be praying for another recession," he added, saying Britain faced a "Spitfire moment" when ministers should immediately intervene to ensure all energy capacity was available for use as soon as possible, with a particular emphasis on mothballed gas-fired power stations.

The comments from Armitt, who is credited with rescuing Britain's rail infrastructure when he was chief executive of Network Rail, were rejected by the manufacturers' organisation EEF, as well as by the National Grid, which runs most of England's pipes and pylons, and the government.

A spokesman for EEF said it shared Armitt's concern about the lack of investment in new energy infrastructure but said alarmist comments would not help.

"It is extremely irresponsible to say that a blackout would be a good thing. But obviously the government does need to tackle shrinking capacity with an emphasis on price and energy security. It should really prioritise reliable and flexible generation rather than intermittent power such as offshore wind," he said.

A spokeswoman for the Department of Energy & Climate Change also dismissed talk of blackouts. "Our priority is to keep the lights on both in the short and long term," said a spokeswoman. "That is why we have legislated through the Energy Act 2013 to bring on the investment in new energy infrastructure that we need to replace power stations that are closing down.

"To increase security in the short-term, Ofgem and National Grid are consulting on the extension of measures that already exist to balance supply and demand. As a longer-term solution, we are introducing a Capacity Market in 2014 which will ensure new capacity is online by the winter of 2018-19."

Tom Greatrex, shadow energy minister, said: "Sir John Armitt is right to point out that the collapse in investment in clean energy since David Cameron became prime minister has put pressure on our energy infrastructure.

"Currently no single institution has responsibility for establishing our future energy needs or developing a strategy to meet them. The next Labour government will create a dedicated energy security board with statutory responsibility for providing advice to government and parliament on Britain's future energy needs and how best to meet them."

The National Grid said it too agreed with Armitt that new investment was needed but said it believed the system could cope.

"Margins are tighter this year than in previous years, but our view is that the market has the capability to meet electricity and gas demand this winter," said a spokesman. "We successfully managed similar levels back in 2008-08. We will continue to keep a watchful eye on the situation and take the necessary actions to keep the lights on."

As a blast of Arctic weather was set to sweep in, Mark Todd, director of the price comparison site energyhelpline.com, urged customers to search for cheaper suppliers. "Thermometers are set to take a plunge this weekend as Britain enters a period of chilly Arctic weather, forcing households to turn up their heating.

"Customers ought to think about preparing for the cold weather ahead by switching their energy tariff now to avoid crippling energy bills," he said.